JERUSALEM (CNN) --Israeli tanks, troops and helicopters remained in northern Gaza early Friday to thwart Qassam rockets from being fired from the region, according to the Israel Defense Forces.

The soldiers set up positions Thursday night overlooking Beit Hanoun and the Jabaliya refugee camp, according to the IDF, a day after a military offensive there left 11 Palestinians dead and wounded more than 100 others, Palestinian hospital officials said.

During the overnight operation, the IDF said its soldiers were fired upon and returned fire, although there were no reports of casualties.

Separately, Israeli security forces early Friday arrested 16 Palestinians in the West Bank.

Palestinian security sources said as many as 50 Israeli tanks and military vehicles were seen in northern Gaza.

The militant group Hamas claimed responsibility for firing three Qassam rockets into northern Israel on Thursday. The rockets landed near the town of Sderot but did not injure anyone.

The Palestinian-built Qassam rockets have a range of six to 10 kilometers -- sufficient to hit Israeli cities if fired from the West Bank.

The Israeli incursion into Jabaliya was launched late Wednesday hours after a Palestinian suicide bomber blew himself up on a bus in the northern Israeli port city of Haifa, killing 15 Israelis.

Palestinian officials blamed Israel for launching a "revenge attack" in Jabaliya in retaliation for the bus attack, but Israeli officials said the soldiers were responding to fierce resistance from armed Palestinians and Thursday's operation was part of Israel's ongoing fight against terrorism.

Israel said the bulk of the Palestinian casualties occurred when a Palestinian explosive device detonated in a building during the Israeli military operation.

Palestinian witnesses said the Israeli forces fired a tank shell into a crowd of unarmed Palestinians, killing eight. The witnesses said the civilians had gathered to watch civil defense units fight a fire.

Three other Palestinians were killed in the initial onset of violence, Palestinian sources said.

Family members in the Druse village of Daliat el-Carmel, Israel, mourn 13-year-old Kmar Abu Khamed, one of 15 people killed in the Haifa bus bombing.

Elsewhere in the troubled region, the Palestinian Red Crescent said a 52-year-old Palestinian woman was killed during clashes with IDF soldiers in Jaba village, near Jenin in the West Bank, and a 16-year-old Palestinian was killed by Israeli gunfire in Nablus. The IDF is checking the reports.

A spokesman for Hamas lauded Wednesday's suicide attack -- which Israeli officials said was carried out by a Hamas militant -- but the group did not officially claim responsibility for the bombing, which gutted the suburban bus in Haifa. (Full story)

The bus was carrying many high school and college students.

Among the 15 dead were a 13-year-old boy and girl, and two Israeli soldiers, authorities said.

The U.S. State Department has labeled Hamas, a Palestinian Islamic fundamentalist group, a terrorist organization. The group's military wing, Izzedine al Qassam, has admitted responsibility for terror attacks against Israeli civilians as well as attacks against the Israeli military.